Permanent testing of acoustic transducers, such as speakers, during normal operation faces several problems. Especially in medical devices (e.g. a portable or a stationary patient monitors) with their alarming function, the audio output of such medical devices must not be influenced or even stopped while testing the functionality of an incorporated speaker. It is desirable that audio signals (e.g. alarm tones) are not delayed or corrupted by the test. False test results of a speaker check caused by normal audio output must be prevented. Moreover, due to the operational area of medical devices, any disturbing noise audible to a patient is not acceptable and should be prevented.
An integrated circuit (LM48100Q, http://www.ti.com/product/lm48100q) has been proposed, that provides a combination of a power amplifier and a corresponding test circuit. The integrated circuit is adapted to sense the load condition as well as detecting open circuit conditions. However, the test is only possible when no other audio signal (e.g. coming from a medical device) is present at the speaker. It even stops current audio output and produces audible noise while testing.